Multifocal lenses, a bespoke product
Εικ. 1
Σχηματική απεικόνιση της προοδευτικής αλλαγής των διοπτριών από τη μακρινή έως την κοντινή όραση σε ένα πολυεστιακό φακό οράσεως
Multifocal lenses offer to the user the ability to use one pair of glasses to see far away (driving, TV), middle distance (PC, cooking) ans short distance (reading). To achieve this the διοπτρική (??) power of the lenses varies progressively to ensure comfortable & smooth transition to the various focal lengths whether we look at a distant object, read a book or work on a PC.(Pic. 1).
Multifocal glasses are an invaluable tool for all those that need glasses both for long and for short distances. In such cases tηε more conventional solutions are either two sets of glasses a pair of bifocals (with the characteristic “window”). These two solutions offer correction for long distance vision (longer than 80 cm) and short distance vision (less than 40 cm) but they leave a gap in between, middle distance vision (Pic. 2).
How many times haωε occured to us to be unable to clearly read a text on a computer screen, the labels on super market shelves or to see details on a work bench or the kitchen?Those that have come face to face with similar problems have concluded that neither long vision glasses, nor short distance glasses or even bifocals offer a solution. On top of everything practical reasons make the use of two pairs of glasses difficult.(Do you loose your glasses just as you pick up a book?)
Εικ.2
Στην παραπάνω εικόνα φαίνεται καθαρά η περιοχή της ενδιάμεσης όρασης. Τα πολυεστιακά γυαλιά είναι η ιδανική λύση ώστε ο διοπτροφόρος να έχει τέλεια όραση σε όλες τις αποστάσεις.
The above examples are useful in understanding the usefulness of a multifocal pair of glasses. In recent years the optical performance of multifocal lenses has inproved substantially thanks to the use of digital technology in their construction. This technology allows accuracies up to 0,01D in the rendition of the lens prescription and take into account how the wearer wears the glasses. More specifically, in lens construction, the following are taken into account: the ophthalmologist‘s prescription, the distance between the eye and the glasses , the slope of the frame in relation to the face η γωνία μετώπης του σκελετού and the use of the glasses. These parameters determine the final διοπτρική δύναμη of the lenses so that the final correction is the one measured by the ophthalmologist. For this reason digitally made, bespoke, multifocal glasses do not have the precise διοπτρική διόρθωση of the prescription. This happens because they are constructed in such a way that when the wearer wears the glasses the correction is exactly the one written down in the ophthalmologist’s prescription. The difference in optical quality is immediately noticeable in long distance vision, short distance vision and in peripheral vision as the astigmatic aberrations in the surface of the multifocal lens are minimized, resulting in high definition vision and expanded field of view. The lenses are constructed in full accordance with the wearer’s proscription and the measurements that the optician give to the factory. This way the wearer has a pair of glasses perfectly matched to his/hers needs. (which means that trying on a friens’s multifocals is meaningless). For the effective operation of multifocal lenses the precise measurements of the above parameters, their application and the wearer’s training in their use is the optician’s responsibility. In additi0n the optician -based on the prescription and after some mathematical calculations -is in a position to advice you as to which multifocal lens ia most appropriate. It cannot be stressed enough that your optician is the person with the full knowledge concerning the application and prorerties of multifocal lenses.
The last but not least factor in purchasing a multifocal pair of glasses is, of course, cost. Six years ago our establishment obtained direct access to a UK lens factory (ie we got rid of the intermediaries) resulting in our ability to offer digitally processed, multifocal lenses in very competitive prices..It will be our pleasure to help with any questions about the application, manufacture and use of multifocal lenses.
